It is well understood that high quality consumer scanners and color ink-jet printers have ushered in an age of unparalleled document counterfeiting. Nowhere is this threat more serious that in connection with counterfeiting of banknotes.
A number of techniques have been proposed to deal with this threat. Yet none has proved wholly successful.
Some techniques, for example, require use of forensic detection equipment to search for the presence of chemical or magnetic tracer elements to distinguish an original from a reproduction. Others require close inspection of a document to discern, e.g., a missing security thread.
In accordance with a preferred embodiment of the present invention, a printed document is provided with a feature that is readily discernable by casual visual inspection, yet is impractical to duplicate using commonly available scanning and printing technology. In one such embodiment, the feature is an optical illusion of a 3D surface on the planar document surface.
The foregoing and other features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.